The implantable defibrillator has been demonstrated to extend patient lives by treatment of potentially deadly arrhythmias. Over time, various efforts have been made to address complications associated with implantation of such devices. For example, early devices generally used epicardial patch electrodes implanted via thoracotomy, with attendant surgical risks and significant risks of failure of the epicardial patch electrodes and associated leads. The use of transvenous leads represented a major advance, avoiding the thoracotomy and improving reliability. However, lead failure remained a significant issue, as the lead attachment in the heart cause the lead to flex with each heartbeat. The advent of subcutaneous defibrillators allows avoidance of these lead failure issues, with leads implanted beneath the skin and over the ribcage of the patient and not subjected to the repeated flexing.
However, subcutaneous defibrillators require higher energy for defibrillation, causing the pulse generators for such systems to be larger than their transvenous predecessors, and both bradycardia pacing and anti-tachycardia pacing to avoid high voltage shock for certain conditions are of limited utility as such pacing subcutaneously can be very uncomfortable for the patient. This has led to interest in further alternative locations for implantable defibrillators, and for other medical devices such as the implantable pacemaker.